Yes,but it is slow. Years ago I made a rounded tapered mandrel that would fight tightly in the casing. The mandrel was then placed in a drill press at moderate speed and Swiss needle files used to shape the rim.
I've since gotten a used Harbor Freight Mini-Lathe and using the same case holding mandrel,shape the rim. 10 times faster and better,consistent results.

Tin Can Sailor
'Nam Vet
NRA Endowment Member
President New Mexico Military Surplus Rifle Pistol Shooters

If you wanna shoot your 8mm Nambu then it's either gonna be easy and expensive or cheap and tedious. You are well advised to thin the rim on .40 S&W brass. I destroyed a perfectly good Nambu extractor with unaltered .40 S&W cases rims.

In my humble opinion, just buy 100 of the Huntington cases and go from there. Yes, at $73 per hundred cases they are a tad pricey but you only cry one time and the low pressure of the 8mm Nambu round means that you can get bunches of reloads out of a case before it gives up the ghost. Grafs has the cases (currently in stock):https://www.grafs.com/retail/catalog/ca ... goryId/500?

Because once-fired .40 S&W cases are so plentiful and free, I so much wanted them to work but they just won't function in my Nambu pistol without modifying the rims, and unlike Rob I can't stand the tedious nature of the work. Plus, the amount of rim work I was doing, when compared to the price of the Huntington brass, meant that I was paying myself something like $2 an hour to endure the tedium of the case prep. Not for me. I highly suggest you just bite the bullet and buy factory cases. YMMV.

One final thought... If you are concerned about the expense then you are not gonna like the price for either a set of 8mm Nambu dies or the odd diameter bullets they require. Sadly, no matter how you slice it Nambu pistols are just more expensive to reload for than either 9mm Luger or .40 S&W unless you cast your own bullets.

.357 SIG would be a slightly better choice than .40 S&W from the standpoint that there would be less forming effort required to make 8mm Nambu cases, but both .357 SIG and .40 S&W have the same nominal rim thickness of .055". And... range pickup .40 S&W cases are usually much easier to find than .357 SIG cases.

Contrast this to the .035" rim thickness of a genuine 8mm Nambu case and you can see there is a pretty substantial difference. Some Nambu pistols have enough clearance between the extractor and bolt face that a .055" rim will work. Others (including mine) do NOT have sufficient clearance and I trashed a perfectly good extractor because I didn't examine my extractor clearance closely enough.

If you don't want to buy the Huntingdon 8mm Nambu cases then I highly suggest you buy a surplus Type 14 extractor and install it for testing so you only trash the replacement extractor and retain your original one undamaged in the event things go south.

I got my replacement extractor from Tom Heller. Great guy and although he specializes in Lugers, he has bunches of old pistol parts (no revolver parts though).